This invention relates to a reproducing method with a magneto-optical recording medium and, more particularly to a reproducing method with a magneto-optical recording medium including, for example, recording and reproducing layers so that the microscopic domain can be recorded into the recording layer during recording and the recorded magnetic domain of the recording layer be expanded and transferred into the reproducing layer during reproduction.
Furthermore, the invention is concerned with a reproducing method and magneto-optical disk apparatus which reproduces a signal by optimally setting a laser light power level during expanding and reproducing the magnetic domain, wherein the magneto-optical disk apparatus performs signal recording and/or reproducing by using laser light and magnetic field applied to the magneto-optical recording medium.
Attentions have being drawn to magneto-optical recording mediums as rewritable recording mediums that are high in memory capacity and reliability. They have being put into practical use as computer memories, etc. Meanwhile, standardization has being put forward for magneto-optical recording mediums having a recording capacity of 6.0 G bytes toward a standard of AS-MO (Advanced Storage Magneto-Optical disk). It has been a practice to reproduce a signal from a high-density magneto-optical recording medium as mentioned above by an MSR (Magnetically Induced Super Resolution) method that irradiates laser light form a detection window in the reproducing layer of the magneto-optical recording medium so that a magnetic domain is transferred from the recording layer into the formed detection window, thereby carrying out signal reproduction.
Meanwhile, a technology of expanding and reproducing a magnetic domain has been developed, wherein alternating magnetic field is applied during reproducing signals from a magneto-optical recording medium so that the magnetic domain present in the recording layer can be expanded and transferred to the reproducing layer by the applications of laser light and alternating magnetic field, thus reproducing signals. There has been an proposal on a magneto-optical recording medium utilizing this technology to record and/or reproduce a signal of 14-G bytes.
The recording/reproducing apparatuses for a magneto-optical recording medium of this kind have been disclosed, for example, in Japanese Laid-open No. H6-295479 (Oct. 21, 1994) [G11B 11/10], Japanese Laid-open No. H8-7350 (Jan. 12, 1996) [G11B 11/10] and so on.
The magneto-optical recording medium 10, as shown in FIG. 1, includes a recording layer 14 and reproducing layer 16 formed by respective magnetic layers on a substrate 12. An intermediate layer 18 is formed between the recording layer 14 and the reproducing layer 16 while a protection layer 20 is formed on the recording layer 14. Incidentally, although the intermediate layer 18 herein is formed by a non-magnetic layer, it may be made by a magnetic layer. Also, the recording layer 14 and reproducing layer 16 can be formed of arbitrary known magnetic materials.
Referring to FIG. 2, microscopic record magnetic domains are recorded within the recording layer 14 of the magneto-optical recording medium 10 through the use of a magnetic head (not shown). During reproduction, the record magnetic domain 22 of the recording layer 14 is transferred into the reproducing layer 16 by illuminating laser light 24, as shown in FIG. 3.
Specifically, laser light 24 provides a temperature profile to the magneto-optical recording medium 10 as shown in FIG. 3. The temperature is highest at around a spot center but gradually decreased toward an outward thereof. It should be noted that, where the magneto-optical recording medium is for example a disk, the temperature profile is different in slant between forward and backward with respect to a moving direction of the magneto-optical recording medium. The temperature gradient is steeply slanted in a region of the disk entering into the laser spot as compared to that of a region exiting therefrom. By utilizing such a temperature profile, the magneto-optical recording medium 10 is increased in temperature up to a desired point.
Referring back to FIG. 2(A), if laser light 24 is illuminated onto the magneto-optical recording medium 10, the magneto-optical recording medium 10 is raised in temperature in accordance with the temperature profile as shown in FIG. 3. The reproducing layer 16 herein is formed by a magnetic layer that, at from room temperature to the Curie temperature Tc, is enriched in transition metal and assumes a perpendicular magnetic anisotropy film. Consequently, if laser light 24 is illuminated, the reproducing layer 16 is increased in temperature, being decreased in coercivity. Due to this, the record magnetic domain 22 within the recording layer 14 is transferred into the reproducing layer 16 through the intermediate layer 18 due to static magnetic coupling. Thus, a transferred magnetic domain 26 is formed within the reproducing layer 16. The transferred magnetic domain 26 is formed in a position corresponding to the record magnetic domain 22.
After forming a transferred magnetic domain 26 in the reproducing layer 16, an external magnetic field Hex as shown in FIG. 2(B) is applied through a not-shown magnetic head. This external magnetic field Hex is of an alternating magnetic field. This alternating magnetic field is applied for at lease 1 period, preferably 2-4 periods while one magnetic domain is passing through a hot spot 24a formed due to the laser light 24. The alternating magnetic field, or external magnetic field, if applied in the same direction (same polarity) as that of the transferred magnetic domain 26, causes the transferred magnetic domain 26 to expand in its diameter, thus forming expanded magnetic domains 26a and 26b. This results in transfer and expansion of the record magnetic domain 22. The transferred magnetic domain 26 with the expanded magnetic domains 26a and 26b are irradiated by laser light for reproduction through the optical head (not shown). Thus, a state is reproduced of magnetization within the reproducing layer 16, i.e. record signal.
In this manner, in the conventional magneto-optical recording medium recording/reproducing apparatus, irradiation of laser light is with an intensity that can cause transfer of a magnetic domain from the record layer into the reproducing layer.
For such a case, according to the experiments conducted by the present inventors, when only laser light was illuminated for reproduction without applying an alternating magnetic field Hex, a reproduced signal obtained had a waveform as shown in FIG. 4(A). In this state, when an alternating magnetic field was applied, a reproduced signal obtained had a waveform as shown in FIG. 4(B). However, the reproduced signal of FIG. 4(B) is not satisfactorily high in level. Thus, there has encountered a limitation in reproducing a signal when the record density is to be tried to increase.
It is therefore a primary object of the present invention to provide a novel apparatus and method for reproducing with a magneto-optical recording medium.
Another object of the invention is to provide a apparatus and method for reproducing with a magneto-optical recording medium which is capable of increasing the intensity of a reproduced signal.
Still another object of the invention is to provide a method for reproducing with a magneto-optical recording medium and magneto-optical disk apparatus which can optimally set a power level of laser light.
A reproducing apparatus according to the present invention is a reproducing apparatus for a magneto-optical recording medium to transfer, during reproduction, a magnetic domain recorded within a recording layer into a reproducing layer, characterized in that a magnetic domain is transferred with expansion from the recording layer to the reproducing layer by applying alternating magnetic field to the magneto-optical recording medium in a state that the predetermined intensity of laser light is illuminated to the magneto-optical recording medium.
A reproducing method according to the invention is a method of reproducing with a magneto-optical recording medium to transfer, during reproduction, a magnetic domain recorded within a recording layer into a reproducing layer, comprising: (a) illuminating laser light with a predetermined intensity not to cause transfer of the magnetic domain from the recording layer to the reproducing layer; and thereafter (b) applying alternating magnetic field to the magneto-optical recording medium, whereby the magnetic domain is transferred with expansion from the recording layer to the reproducing layer.
The magneto-optical recording medium is formed with a particular region, for example, for each sector or zone. This particular region is previously formed with a signal to adjust an intensity of laser light to be illuminated to the magneto-optical recording medium through the optical means.
In this invention, the optical means includes an intensity adjusting means to set a laser light intensity to a degree that the signal of the particular region cannot be reproduced only by laser light. Laser light thus adjusted in intensity is illuminated through the optical means to the magneto-optical recording medium. Thereafter, a magnetic field applying means applies magnetic field to the magneto-optical recording means. As a result, the record magnetic domain recorded in the recording layer of the magneto-optical recording medium is transferred with expansion to the reproducing layer. That is, if alternating magnetic field is applied in a state that laser light is illuminated with an intensity at which no transfer of the record magnetic domain can be caused to the reproducing layer, there occur concurrent transfer and expansion of the record magnetic domain to the reproducing layer. As a result, the record magnetic domain is transferred with expansion.
According to this invention, because transfer and expansion of a magnetic domain is effectively made from the recording layer to the reproducing layer, a reproduced signal is increased in level. Consequently, the record magnetic domain in the recording layer can be reduced in size, enabling recording with higher density.
A second reproducing method according to the invention is a method of reproducing a signal from a magneto-optical recording medium by using laser light and an alternating magnetic field, including a first step and a second step. In the first step, a power level of laser light is determined based on a reproduced signal obtained by reproducing from the magneto-optical recording medium with using laser light and alternating magnetic field, and on a record signal. In the second step, a signal is reproduced from the magneto-optical recording medium by using the laser light set at a power level determined by the first step and an alternating magnetic field.
According to the second reproducing method, the record signal recorded in the magneto-optical recording medium is reproduced by magnetic domain expansion so that a power level of laser light is determined based on the reproduced signal and record signal. It is therefore possible to accurately determine a power level. Further, magnetic domain expansion and reproduction can be made suited for a loaded magneto-optical recording medium.
A third reproducing method according to the invention is a method for reproducing a signal from a magneto-optical recording medium by using laser light and alternating magnetic field, including a first step, a second step, a third step and a fourth step. In the first step, a predetermined record signal is recorded to the magneto-optical recording medium. In a second step, the signal recorded in the first step is reproduced while changing a power level of laser light. In the third step, a signal reproduced in the second step is compared with the record signal and determining a power level of laser light at which the reproduced signal is substantially coincident with the record signal. In the fourth step, a signal is reproduced from the magneto-optical recording medium by using laser light set in the power level determined in the third step and alternating magnetic field.
According to the third reproducing method, a predetermined record signal is actually recorded in a magneto-optical recording medium. A power level of laser light to be illuminated is determined such that a reproduced signal, obtained by performing magnetic domain expansion and reproduction on the recorded signal while changing laser light power level, becomes coincident with the record signal. Accordingly, even where the magneto-optical recording medium loaded is not recorded with a signal to determine a laser light power level, it is possible to accurately determine a power level suited for the loaded magneto-optical recording medium. Also, accurate magnetic domain expansion and reproduction are possible using a determined power level of laser light.
A fourth reproducing method according to the invention is a method of reproducing a signal from a magneto-optical recording medium by using laser light and alternating magnetic field, including a first step, a second step, a third step and a fourth step. In the first step, a predetermined record signal is recorded in a calibration region provided in the magneto-optical recording medium. In the second step, the record signal is reproduced from the calibration region while changing a power level of laser light, by using laser light and alternating magnetic field. In the third step, a signal reproduced in the second step is compared with the record signal and determining a power level of laser light at which the reproduced signal is substantially coincident with the record signal. In the fourth step, a signal is reproduced from the magneto-optical recording medium by using laser light set in the power level determined in the third step and alternating magnetic field.
According to the fourth reproducing method, the magneto-optical recording medium has a calibration region. The calibration region is actually recorded with a predetermined record signal so that magnetic expansion and reproduction is made on the recorded signal to determine a power level of laser light for signal reproduction. Accordingly, a power lever of laser light to be illuminated for reproduction can be determined without using a region to be recorded with a signal. Also, if a calibration region is placed such that laser light reaches a usual signal recorded region after passing the calibration region, it is possible to determine a power level of laser light to be illuminated prior to reproducing the usual signal. Furthermore, where a plurality of calibration regions are provided in a radial direction of the magneto-optical recording medium, even if the magnetic material be uneven in magnetic characteristic over a disk substrate, magnetic domain expansion and reproduction can be implemented in a manner suited for the magnetic characteristic.
Incidentally, in the third and fourth reproducing methods, the change in laser light power level in the second step is desirably performed within a range that no magnetic domain transfer is made only by laser light from the recording layer to the reproducing layer. By doing so, a laser light power level is determined within a range that no magnetic domain transfer is made only by laser light from the recording layer to the reproducing layer. It is therefore possible to accurately determine a power level suited for magnetic domain expansion and reproduction.
A magneto-optical disk apparatus according to the invention is a magneto-optical disk apparatus for recording and/or reproducing a signal to and/or from a magneto-optical recording medium by using laser light and magnetic field, comprising: a determination circuit for determining a power level of laser light based on a predetermined record signal and a signal reproduced of the predetermined record signal from the magneto-optical recording medium by using laser light and alternating magnetic field.
In this magneto-optical disk apparatus, the determination circuit determines a power level of laser light based on a signal reproduced using laser light and alternating magnetic field as well as a record signal as a basis of the reproduced signal. Accordingly, it is possible to promptly and accurately determine whether the reproduced signal is correct or not. As a result, a laser light power level can be determined with rapidity and accuracy.
A second magneto-optical disk apparatus according to the invention is a magneto-optical disk apparatus for recording and/or reproducing a signal to and/or from a magneto-optical recording medium by using laser light and magnetic field, comprising: a determination circuit for determining a power level of laser light based on the reproduced signal while changing the power level of laser light such that a signal produced of the record signal becomes substantially coincident with the record signal.
According to the second magneto-optical disk apparatus, the loaded magneto-optical recording medium is previously recorded with a signal to determine a laser light power level suited for magnetic domain expansion and reproduction. The recorded signal is reproduced by magnetic domain expansion while changing the laser light power level. If the power of laser light is too intense or weak, there is no agreement between the reproduced signal and the record signal. The determination circuit determines, as an optimal laser light power level, a power level that the reproduced signal substantially agrees with the record signal. It is therefore possible to determine an optimal laser light power lever with rapidity. Thus, a power level can be determined suited for the loaded magneto-optical recording medium.
A third magneto-optical disk apparatus according to the invention is a magneto-optical disk apparatus for recording and/or reproducing a signal to and/or from a magneto-optical recording medium by using laser light and magnetic field, comprising: an optical head, a magnetic head and a determination circuit. The optical head illuminates laser light to the magneto-optical recording medium and detects reflection light thereof. The magnetic head applies magnetic field to the magneto-optical recording medium. The determination circuit determines a power level of laser light based on a record signal in the magneto-optical recording medium and a reproduced signal of the record signal detected by the optical head while applying alternating magnetic field through the magneto-optical head and changing a power level of laser light, so that the reproduced signal becomes substantially coincident with the record signal.
According to the third magneto-optical disk apparatus, the alternating magnetic field for determining a laser light power level is applied through the magnetic head to the magneto-optical recording medium while laser light is illuminated through the optical head to the magneto-optical recording medium. Even in a structure having a magnetic head and an optical head arranged sandwiching the magneto-optical recording medium, a laser light power level suited for magnetic domain expansion and reproduction can be determined with rapidity and accuracy.
A fourth magneto-optical disk apparatus according to the invention is a magneto-optical disk apparatus for recording and/or reproducing to and/or from a magneto-optical recording medium by using laser light and magnetic field, comprising an optical head, a laser drive circuit, a magnetic head and a determination circuit. The optical head illuminates laser light to the magneto-optical recording medium and detects reflection light thereof. The laser drive circuit drives a laser light source included in the optical head. The magnetic head applies magnetic field to the magneto-optical recording medium. The determination circuit outputs a drive signal to the laser drive circuit to change a power level of laser light to be emitted through the optical head, and determines a power level of laser light based on a predetermined record signal recorded to the magneto-optical recording medium, alternating magnetic field applied through the magnetic head and a signal reproduced of the record signal detected by laser light emitted through the optical head based on the drive signal, so that the reproduced signal becomes substantially coincident with the record signal.
According to the fourth magneto-optical disk apparatus, a drive signal is outputted from the determination circuit to the laser drive circuit, to change a power level of laser light to be emitted through the optical head. Based on the drive signal, the laser drive circuit drives a laser light source included in the optical head so that laser light different in power level is illuminated to the magneto-optical recording medium. Consequently, a reproduced signal can be detected by performing magnetic domain expansion and reproduction while changing the power level on the magneto-optical recording medium. Based on the reproduced signal, a power level of laser light is determined. As a result, it is possible to accurately determine a laser light power level.
A fifth magneto-optical disk apparatus according to the invention is a magneto-optical disk apparatus for recording and/or reproducing a signal to and/or from a magneto-optical recording medium by using laser light and magnetic field, comprising an optical head, a laser drive circuit, a magnetic head, a magnetic head drive circuit and a determination circuit. The optical head illuminates laser light to the magneto-optical recording medium and detecting reflection light thereof. The laser drive circuit drives laser light source included in the optical head. The magnetic head applies magnetic field to the magneto-optical recording medium. The magnetic head drive circuit drives the magnetic head. The determination circuit outputs to the magnetic head drive circuit a first drive signal to record a predetermined record signal in the magneto-optical recording medium and to the laser drive circuit a second drive signal to change a power level of laser light to be emitted through the optical head, and determines a power level of laser light based on a predetermined record signal recorded based on the first drive signal, alternating magnetic field applied through the magnetic head, and a signal reproduced of the record signal detected by laser light emitted through the optical head based on the second drive circuit, so that the reproduced signal becomes substantially coincident with the record signal.
According to the fifth magneto-optical disk apparatus, the determination circuit outputs to the magnetic drive circuit a first drive signal to record a predetermined record signal for determining a laser light power level. Based on the first drive signal, a predetermined record signal is recorded on the magneto-optical recording medium. Also, the determination circuit output to the laser drive circuit a signal to change the laser light power level. The laser drive circuit drives a laser light source in the optical head based on the second drive signal. Thus, laser light different in power level is illuminated to the magneto-optical recording medium, reproducing the predetermined record signal through magnetic domain expansion. Accordingly, even where the loaded magneto-optical recording medium is previously not recorded with a predetermined record signal, it is possible to rapidly and accurately determine a laser light power level suited for the loaded magneto-optical recording medium.
In the fifth magneto-optical disk apparatus, the determination circuit, after loading the magnet-optical recording medium, outputs to the magnetic head drive circuit a first drive signal to record a predetermined record signal for determining a laser light power level after loading the magneto-optical recording medium but before recording the record signal, and to the laser drive circuit a second drive signal to change the power level of laser light to be emitted through the optical head before reproducing the record signal. By doing so, prior to recording a usual signal, a first drive signal is outputted from the determination circuit to the magnetic head drive circuit to record the predetermined record signal for determining a laser light power level. Based on the first drive signal, the predetermined record signal is recorded on the magneto-optical recording medium. Also, a second signal is outputted from the determination circuit to the laser drive circuit to change the laser light power level. Magnetic domain expansion and reproduction is made on the predetermined record signal already recorded while changing the laser light power level. Based on a signal reproduced, a laser light power level is determined. Accordingly, it is possible to positively determine a laser light power lever suited for magnetic domain expansion and reproduction before reproduce operation on the usual signal. Thus, the usual signal can be accurately effected of magnetic domain expansion and reproduction.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.